The morphology of the small intestines of heavy (Arbor Acres) and light (Lohman) chicks was determined posthatch in parallel with digestion, enzyme secretion, and passage time. Villus height and volume increased from 4 to 10 d, particularly in the jejunum and ileum. The number of enterocytes per villus increased with age, but enterocyte density was greater in jejunum than ileum. Villus volume and enterocyte density was greater in Arbor Acres than Lohman chicks from hatching and the rate of change with age was similar in both strains. Enzyme secretion to the duodenum was higher per gram of feed intake in heavy-strain birds on Day 4 after hatching but thereafter no differences were apparent. Passage time was 50% shorter in light-strain chicks on Day 4 but the difference between the strains was not significant from Day 10. No differences in fatty acid digestion were observed with age or between strains. Nitrogen digestion increased in both strains from approximately 70% on Day 4 to close to 90% on Day 14. Starch digestion was 90 to 95% from 4 to 14 d in Arbor Acres birds, but increased from approximately 80% on Day 4 in Lohman chicks to 93% on Day 14. Feed intake may determine the amount of uptake in posthatch chicks.